There are two conventional approaches for user equipment (UE) initiated uplink (UL) transmission in a wireless system. In one approach the UE may transmit a scheduling-request (SR) to the base station (BS), and in response the base station allocates UL resources and then informs the UE about the allocated UL resources by transmitting a UL grant signal to the UE. This type of UL resource allocation may be referred to as “scheduled-based UL access” (also referred to as the “scheduled-based method” or a “grant-based method”). In a second approach, the UE may transmit its data signals within an assigned set of UL resources that is pre-defined by the base station. This type of UL access may be referred to as “grant-free UL access” (also referred to as the “grant-free method”).
There is a trade-off between latency and resource utilization efficiency in both the grant-free method and the scheduled-based method. In the grant-free method, a pre-defined amount of resources is allocated with a pre-defined periodicity. This type of allocation may have lower latency with a cost of resource under-utilization if the UEs do not have anything to transmit. On the other hand, the scheduled-based method may improve the resource-utilization efficiency with a cost of higher latency as it takes multiple time-slots to receive the UL grants at the UE. As a consequence, both of these conventional methods may not be satisfactory for delay-sensitive applications (e.g., critical industrial control, remote surgical robots, etc.) or other applications. These applications are generically referred to as “ultra reliable low latency communication” (URLLC) in the industry.